DENVER (AP) — Old Denver pulsed with H2O, water that snaked through the creeks and irrigation canals crisscrossing Colorado’s high prairie before 150 years of urban development buried most of them or forced them into pipes.

New Denver wants those waterways back.

City leaders are ramping up what they describe as a massive, restorative “daylighting” of buried water channels wherever possible — cutting through pavement and re-engineering old streams and canals to create up to 20 miles of naturalistic riparian corridors. Hundreds of millions of dollars have been committed. Eventual costs are expected to top $1 billion over several decades. This work reflects increased interest worldwide in harnessing water and natural processes to make cities more livable.

Starting in 1858 with the discovery of gold in Colorado’s mountains, Denver developers focused on filling in creeks to make way for the construction of railroads, streets, smelters and housing — all laid out across a grid imposed on the natural landscape. The 184-page Green Infrastructure Implementation Strategy that Mayor Michael Hancock’s administration issued this summer reverses that approach with an inventory of high-priority projects aimed at — to the extent that booming growth and development will allow — reopening and revitalizing waterways.

“It is like undoing history,” project manager Patrick Riley said last week along a newly formed 1,000-foot stretch of Montclair Creek — already attracting geese as big trucks beeped and contractors in neon green vests re-contoured the urban terrain.

The Montclair Creek project marks Denver’s most ambitious and controversial daylighting so far, a $298 million revival of a waterway that flows 9 miles from high ground at Fairmount Cemetery (elevation 5,485 feet) under the north half of the city. Work crews are excavating and rerouting water, digging holes for ponds, and planting native grasses and perennials in four areas: the 130-acre City Park Golf Course, the Park Hill Golf Course, a 1.2-mile greenway along 39th Avenue, and a landscaped “outfall” through a 5-acre Globeville Landing park near the South Platte River (elevation 5,274 feet) west of the Denver Coliseum.

City engineers say that, by reconstructing the urban landscape where possible, they’ll slow down water, filter it through vegetation to remove contaminants, control storm runoff and nourish greenery to help residents endure the climate shift toward droughts and rising temperatures.

“The city is taking a new approach,” said Sarah Anderson, water quality director in the public works department, who is helping drive Denver’s move from gray to green.

“A concrete channel does zero for water quality. It’s that old idea of getting stormwater away from property as quickly as you can,” Anderson said.

While a lack of open land and neighborhood resistance can limit daylighting of long-squelched creeks and canals, increasing volumes of storm runoff — the result of the paving of more and more of the city — require action.

The U.S. Army Corps of Engineers has supported daylighting, recognizing that pipes and concrete channels typically can’t handle surges the way natural creeks and floodplains once did before development.

“We’re trying to piece it together over time, to open up these streams,” Anderson said. “But it is going to take a very long time.”

Other projects in the works:

— Re-exposing a southern branch of Montclair Creek that flows under an area extending from City Park across Colorado Boulevard and eastward along Hale Parkway.

— A $77 million removal of concrete and widening of the Weir Gulch that runs through southwestern Denver from South Sheridan Boulevard to the South Platte River.

— A $26 million revitalization of Harvard Gulch in south-central Denver.

— The $249 million enhancement of the South Platte, reshaping and widening river banks between Sixth and 58th avenues, to create an ecosystem healthy enough for trout to reproduce through Denver.

— Converting portions of the 71-mile High Line Canal irrigation system, built in 1883 and owned by Denver Water, into a greenway and refuge.

— Other waterway projects that city officials are discussing involve naturalistic re-engineering of concrete trapezoidal channels in Montbello, flood-prone gullies in Globeville, the southwestern Sanderson Gulch, and buried channels citywide where alluvial sediment indicates creeks once flowed before settlers arrived.

“It is the right thing to do,” said city stormwater engineering supervisor Bruce Uhernik, a private sector veteran who previously dealt with drainage around Denver’s zoo. “We are ramping up. We haven’t hit our peak.”

For decades, waterways in Denver “were looked at as something that needed to be channelized, made smaller, so that we could build properties right up against them,” Uhernik said. “We confined. We restricted. We made these urban waterways more ditch-like than river-like. It wasn’t good practice. It was good for moving water and to build, but not for habitat.”

The new approach will enable a healthier environment, he said.

“We’re just trying to take back that space and make waterways more natural and more beautiful. Why would people not want something to be more natural? This is being responsible — not just to what the city and people need, but to the environment’s needs. Birds. Fish. Trees that should be growing along these corridors. All these work in unison. If you break the chain, things fall off course.”

Denver innovations include installing an ultraviolet water-cleaning station at the Montclair Creek outfall to boost natural processes in zapping chemical contaminants, an expanding array from antibiotics to antidepressants, before water reaches the South Platte.

Along Brighton Boulevard north of downtown, city crews also built 56 cement boxes, designed to hold native grasses and flowers in a replaceable soil mix that includes ground-up newspaper, to filter runoff water so that less pollution reaches the South Platte.

Around the world, a growing movement to revive urban waterways by incorporating natural processes has gained momentum in recent years with daylighting projects in Seattle, Washington, D.C., Kalamazoo, Michigan, and Seoul, South Korea. But few cities in the arid West, other than Los Angeles and Denver, have embarked on citywide re-engineering. In the booming West, water scarcity and a climate shift toward worse droughts and extreme storms increasingly complicate urban growth and development.

Denver took first steps toward bringing back naturalistic waterways around 2002 after the dismantling of Stapleton International Airport. Demolition of concrete runways revealed a Westerly Creek that had been straight-jacketed through a 108-inch pipeline. City parks and public works crews seized the opportunity to resurrect a wetland, and, in 2016, finished opening the creek, which flows into the degraded Sand Creek that weaves through industrial wasteland past a fossil fuels refinery to the South Platte.

When heavy rain hit the re-engineered, recreation-oriented Westerly Creek area in 2013, potentially ruinous torrents soon slowed and sank into the wetlands.

North Denver residents in Park Hill and other neighborhoods nevertheless fought the restructuring of Montclair Basin waterways. Community activists complained that city officials secretly hatched the project (dubbed “Platte to Park Hill”), with its construction of detention ponds on golf courses, with a primary motivation of enabling a contentious overhaul of Interstate 70 that requires flood control.

Instead of state-of-the-art urban design that could best absorb increased storm runoff, Denver’s reconstructed Montclair Creek looks more like “a big old-fashioned drain” that is “not really naturalistic . more like an engineered channel,” with the City Park and Park Hill golf course ponds destined to become “huge trash-catchers,” said Bridget Walsh, a board member of City Park Friends and Neighbors. “Is it going to be a golf course or a swamp?”

But those opponents also are directly affected by increased flooding of streets because storm runoff, funneled through a 10-foot-diameter pipeline installed in 1933, exceeds the system’s capacity. Too much water flows too fast off streets due to the diminishing permeability of the city.

“I hope they do it right,” said geologist Denny LeMar, 62, working in his yard a block north of the City Park Golf Course as excavators dug out a detention pond. He’d understood from a neighborhood news article that the I-70 project’s needs were dictating city storm runoff remedies. He raised the issue of mosquito control if more urban waterways are exposed.

Yet LeMar said he’s hopeful that the daylighting of Montclair Creek will reduce flooding, and he was delighted to see Canada geese returning to new vegetation on the reconfigured golf course. “The jury is still out.”

Historic Denver maps from the late 1800s show multiple irrigation canals and curving dotted lines denoting unnamed waterways, including a creek that flows through the Montclair Basin from Fairmount Cemetery toward north Denver industrial areas where smelting and rendering plants were located along the South Platte.

City officials said the Montclair Creek daylighting is part of the broader citywide “green infrastructure” push and that enabling the reconstruction of I-70 is one of many side benefits.

Dealing with floods by trying to funnel more and more runoff into culverts and pipelines has become increasingly costly and ineffective, city officials said. A recent city study estimated that dealing with worsening storms by installing more pipelines would cost taxpayers $1.4 billion.

But it’s unclear whether a new approach of embracing waterways will be cheaper in the long run.

As work crews neared completion of the Montclair Creek outfall by the South Platte, project manager Riley said recreational benefits and a need for places “where water could percolate out naturally” — rather than costs — are driving this push that has unified support from city leaders.

“You have to do what is right for the health of rivers. That’s part of the health of the city,” Riley said. “You are going to see a return to natural processes.”